1. Field of the Invention
The present invention relates generally to gyrotron-traveling-wave-amplifiers and particularly to a folded waveguide, gyrotron-traveling-wave-amplifier capable of producing high power, broadband millimeter wave radiation.
2. Description of the Related Art
Broadening the instantaneous bandwidth (BW &gt;10%) of high power millimeter wave amplifiers remains a critical issue in high power vacuum electronics. Light weight, compactness and low-cost are also important factors to be met for both practical military and commercial applications. Military applications include high resolution radar/communications and electronic jamming equipments. Commercial applications include navigation equipments for airborne and ship-board systems, high efficiency satellite communication systems, low-cost millimeter-wave material processing, millimeter wave imaging systems, and RF test and measurements.
Use of free electron beams (linear beam and rotating beam) in vacuum tubes has been recognized as a promising source of multi-kilowatt high power, broadband millimeter wave radiation, operating at a moderate beam voltage (&lt;60 kV). Uniform waveguide gyro-amplifiers cannot produce an instantaneous bandwidth in excess of 10%, unless the waveguide is loaded so that the wave phase velocity becomes constant over a wide frequency range. Conventional approaches for achieving wideband (BW&gt;10%) RF amplification in gyrotron-traveling-wave-amplifiers are either loading disks or dielectric in the waveguide to slow down the RF phase velocity of the wave or tapering both the waveguide and the external magnetic field along the axial distance. Since the azimuthal and axial beam modulations in the beam-wave interaction of the conventional gyrotron-traveling-wave-amplifier devices compete with each other, the operating frequency band is either in the fast wave region (negative mass instability) or in the slow wave region (Weibel instability). This is one of the main limits to broadening the instantaneous bandwidth. The present inventors do not know of any gyrotron-traveling-wave-amplifiers in the prior art that can be operated simultaneously in both the `fast` and `slow` wave regions, continuously across the light line intersection.